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AB0 indirect or "rebuttal"

Determination AB0 indirect or "rebuttal"

It 's a test complementary and not alternative to direct determination. Its usefulness is mainly limited to the confirmation of the AB0 determined using commercial antisera allowing to interpret the possible, though infrequent, questionable results and to highlight the very rare false negatives and false positives of direct evidence .(....)

The counter is usually performed at the first determination group, while for the future control us is limited to the direct determination.
The indirect test for the presence of A and Anti B antibodies that are naturally present if the fees are absent antigens. To test should have known A and B red cells suspended in fresh saline to 3-4%. The red cell suspension may be stored in the refrigerator for several days. In practice this means having in the area known donors of group A and B available to frequent small blood samples.

Technique:
> mix 2 drops of serum or plasma from blood typing + 1 drop of red blood cells suspended in A or B notes to 3-4% in saline.
> read for agglutination
Even this test can be performed in test tubes (centrifugation and read out as above) or slide, slide, however, this survey is less reliable and requires more time and a closer reading eventually with the aid of a microscope at low magnification.

Expected Results:
° samples / plasma of group A and B red cells agglutinate 0 ° samples
/ plasma of group A red cells agglutinate B
° samples / plasma of group B red cells agglutinate A
° samples / group AB plasma did not agglutinate A or B red blood cells or red blood cells

If you are faced with a discrepancy between direct evidence and rebuttal, and that we are faced with the unexpected positive or negative, will need to make a series of additional tests to explain the reason for the discrepancy. In addition to a simple error in identification / execution of the test are different, but rare, situations that may explain unexpected results, by sub-groups AB0 rare (see the A2 subgroup [1] ) in the presence of autoantibodies cold [ 2] . In these cases to clarify the presence of indirect agglutination test is useful to the unexpected execution of a self [3] .

In general in the case of a recipient whose group AB0 found a discrepancy between direct and indirect evidence should be explained not only transfuse blood donor certainly 0.

Babies and up to 4 months of age do not yet have natural anti-A antibodies or anti-B, in these cases the proof is so often negative and its execution is merely confusing. Unexpected indirect negative test can also be observed in elderly or immunocompromised, in these cases, the absence or weakness of the reactivity is due to the low titer of regular.

A test of indirect confirmation of ABO compatibility of donor and recipient groups is represented by the cross-test at room temperature.


[1] Occasionally the plasma / serum A subgroup of A2 agglutinate red blood cells called type A1 is the most common. These clumps have no clinical significance, therefore the cells A1 can be safely transfused to patients with group A2 in spite of the apparent "incompatibility" [2] Presence of autoantibodies cold: in the case of agglutination of both cells ( A and B) which does not correspond to the direct determination, as expected, a group can be 0 in the presence of autoantibodies active at room temperature (antibodies or Fedde crioagglutinine). In these cases it is useful to add also a test of self-control in such cases will be positive, contrary to what is normally expected. If self-control is positive it is highly likely the presence of cold autoantibodies (that agglutinate at room temperature almost all the cells). These are generally not significant, that is not cause transfusion reactions. In case of positive self-repeating all the tests at 37 ° C by incubating cells and serum / plasma in a water bath. If the agglutination of self disappears (that is no longer active cold autoantibodies) can interpret the residual agglutination with red cells A or B or with those of the donor (during the test cross) as significant. If that persists in the agglutination test cross will be prudent not to transfuse blood and look for another donor. [3] Self-control is carried out for the serum / plasma of the subject plus a 3-5% cell suspension in saline of the same subject. You can perform the technique on a plate, or better, with that tube in the same way as the crusade at RT. Normally red cells do not agglutinate when suspended in their serum / plasma. If you look at macroscopic agglutination This argues in favor of the presence of auto-antibodies or paraproteins (in this case will be observed under the microscope and the stacking of agglutination). A positive self-control requires a careful analysis of the agglutination test may be found in AB0 typing directly and indirectly through the repetition of tests At 37 ° tube.

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